To me they’re usually made, not born, into villains by some misfortune often out of their control. Idealist individuals with no bad intentions initially but we’re so wronged or misunderstood by society that they couldn’t take it anymore and reached a breaking point.

Bram Stoker’s Dracula comes to mind (the 1992 movie version). Dracula was a normal dude who fought for his kingdom until his wife was tricked into thinking he died in a battle, and she committed suicide to be with him. He got pissed when he found out, and even more so when the priests said her soul would be condemned to hell due to killing herself. He vowed to avenge her death through the forces of darkness.